Metal Marking with a Fiber Laser

Lasers are ideally suited to metal marking because they can be easily automated, are non-contact, and utilise no consumables, making them more environmentally friendly than ink based marking. Lasers can be used for a diverse range of metal marking applications within the electronics, automotive, tools, aerospace and medical devices industries.

Pulsed Fiber Lasers have the ability to produce marks of varying sizes and complexities from simple serial alphanumeric codes to more intricate vector or bitmap images. This application insight looks at marking metals with a Pulsed Fiber Laser and focuses on black anneal marking and anodized aluminium marking, and the benefits of Pulsed Fiber Lasers against other technologies.

Introduction

Traditionally metal marking has been carried out using machine marking; ink based printing and chemical etching. Lasers provide a new alternative to these traditional methods and offer several advantages. There are many types of Lasers that can be used for metal marking but Fiber Lasers, which are a more recent technology, are taking an increasing proportion of the market.

Marking with a Pulsed Fiber Laser

Fiber lasers, like our redENERGY G4 Pulsed Laser, are gaining an increasing segment of the market for the following reasons:

Fiber Lasers can be tailored to have a higher beam quality than many other Lasers of comparable average output power. This affects the spot size of the beam which in turn impacts on the feature size (width of mark).

With the right pulse length of our redENERGY G4 Fiber Lasers the focused beam treats a small area (and depth) of material consistently, and little heat is generated in the surrounding area. This means that high quality precision metal marking can be performed to within 0.1 mm of intricate component parts without causing distortion or potential damage to the other parts.

Fiber Lasers also offer no maintenance and are easy to set up and use. This means that comparatively Fiber Lasers have a much lower total cost of ownership.

Practically anything that can absorb Laser light can be marked, however the choice of Laser is usually dependant on the material. Most metals are highly reflective to 10µm and so 1µm is a better wavelength.

There are two main mechanisms by which Lasers can mark metal. The first is where the metal is ablated/vaporised or is melted and re-solidified to give a distinct mark. An example of this is marking of anodised aluminium which is expanded on later. The second mechanism is through thermal processes which includes oxidation and anneal marking, which is explained in the next section.

Black anneal marking

Black anneal marking is a common type of metal marking on stainless steel that can be achieved using Fiber Lasers. An anneal mark is created by enhancing the oxide layer thickness on the surface. This is known as a sub melting point process, which is produced by extremely fine control of time and temperature that the material made is subject to. The image above (Figure 1) illustrates what can be achieved with our redENERGY Pulsed Fiber Laser.

Figure 2: Comparison of Black anneal mark on 304 Stainless Steel

Our redENERGY G4 Pulsed Laser can be smoother than other Q-switched Fiber Lasers (Figure 2). This means there is less damage to the metal surface, which leads to better definition and clearer markings.

Using a defocused multi pass technique our Lasers can be faster than other q-switched Fiber Lasers (Figure 3). However the redENERGY G4 can also be used in focus, a different method of applying the black anneal mark, giving an incredibly fast coverage rate in just one pass (Figure 3 c). However this mark is not as intense as marks made with normal settings but maybe acceptable for many applications.

Anodised Aluminium

Lasers are often used to mark anodised aluminium. The Laser effectively removes the anodised aluminium giving a very high contrast, permanent mark.

Coloured or black anodised aluminium are the most common types marked by Lasers. However it is also possible to mark clear anodised aluminium but this is less common. The interesting point about this type of Laser marking is that either a dark or a light mark can be made dependent on the power of the Laser used.

Our redENERGY Pulsed Lasers offer several advantages in marking anodised aluminium. The Lasers higher repetition rates can take advantage of higher scan speeds and can be up to 50% faster. It can also provide better line definition due to greater spot overlap. The Laser also provides a smoother ablated surface (Figure 4). This is due to the reduced central intensity in the focal spot, which results in less digging to the surface.